1. Field of the Invention
The invention relates to a method for determining the pick-up position of electrical components in a component placement device for populating substrates with the components, which are made ready in pockets of at least one belt, the belt being inserted into a feed module which delivers the components to a pick-up point in a defined pick-up position.
2. Description of the Related Art
Feed modules of this type are usually provided with a pin wheel which, with its radially projecting pins, engages in transport holes in the belt and which is rotated in defined angular steps corresponding to the pitch spacing of the pockets in the belt. The pockets have a defined positional relationship with the transport holes. Centering marks are fitted to the feed modules at the end of the production process, in the area of the pick-up point, which have a defined positional relationship with the pins of the pin wheel and which are intended to compensate for production tolerances.
The feed modules are fixed in a defined position to a component table. Since the centering mechanism for this purpose can be provided only at some distance from the pick-up points, it is possible for positional deviations to occur in the centering marks. A component placement head for handling the components is provided with the CCT camera, which is used to determine the exact position of the substrate to be populated in the component placement device. In order to be able to take into account the previously mentioned positional deviations, it is usual, following the installation of the feed module, to determine the position of the centering marks on the feed module using this printed circuit board camera, with which, because of the defined positional relationships, the position of the component to be picked up can also be determined. Deviations in the drive system caused by operation cannot be eliminated completely in this case.
In the course of modern technologies, the components to be placed are being increasingly miniaturized. It is usual to provide the component placement head with a suction gripper, which is set down on the components to be picked up and which sucks up a component at its end. Here, the gripper has to dip into the pocket in order to be placed on the component. The permissible tolerances between the transport hole and the pocket are so great that the suction gripper making the pick-up cannot with certainty be set exactly onto the component to be picked up; it is placed on the edge of the pocket and, as a result, may miss the component. In this case, however, this is a systematic error, at least over a relatively long section of the belt.
It is usual, in the case of each of the components picked up, to measure their position with respect to the suction gripper and to place the component onto the substrate with a corresponding correction value. In order to be able to determine the systematic error, at least after a belt change, a series of components is removed from the start of the belt and measured, and an average deviation is determined. However, this is a problem when the component is not found during the first attempt at a pick-up. The gripper then has to be moved step by step over the previously mentioned tolerance range until it finds the component.
Furthermore, U.S. Pat. No. 6,154,957 discloses a component placement device with a component placement head to which a camera pointing toward the pick-up points of the components is fixed. According to column 3, lines 15 to 19, this camera is used to detect optically the components lying in the pockets in the belt and to detect their pick-up position. Since, in this case, each positionally critical component is obviously measured before being picked up, the highest possible hit reliability is achieved. Since the camera and the respective suction pipette are at a distance from each other, the component placement head in each case has to be positioned at two different coordinate points in two steps, which is time consuming. A further disadvantage is that the pocket is normally temporarily covered at the removal point by a movable covering slider, whose actuation reduces the time interval for the scanning and the removal.